1. Field of the Invention
The present invention relates to an imaging system capable of synchronizing itself with an external vertical synchronizing signal, an imaging controller for synchronization with the external vertical synchronizing signal, and a method and a program for the vertical synchronization.
2. Description of the Related Art
An imaging device, which produces images of objects and picture signals, produces such images in accordance with an internal synchronizing signal produced by itself. When the imaging device is supposed to synchronize itself with an external device or a TV station, it has to synchronize its internal synchronizing signal with an external synchronizing signal to transmit picture signals to the apparatus or station.
For example, if two or more imaging devices are supposed to synchronize themselves with one another, each imaging device has to have a synchronizing circuit to synchronize itself with a single common external synchronizing signal. Such synchronization is achieved by synchronizing an internal synchronizing signal of each imaging device with the single common external synchronizing signal by using a PLL.
Disclosed in, for example, patent literature 1 is an art to synchronize an imaging device with an external synchronizing signal by using no PLL, but the external synchronizing signal as a reset signal for a horizontal-synchronization counter and/or a vertical-synchronization counter and using a logic circuit alone.
In the case of the invention of patent literature 1, however, if an imaging device is located at a relatively long distance from an imaging controller for relaying an external synchronizing signal to the imaging device, the imaging device is delayed in synchronization by the signal-transmission delay time of the transmission line between the controller and the device. Therefore, only transmission lines within the range of allowable delay time can be constructed. Thus, the length of transmission lines capable of making use of such function for external synchronization is limited.
Patent literature 1: Japanese Patent Unexamined Publication No. 2001-211347